464 ALASKAN GLACIER STUDIES Scott Glaciers whose relationships, where crossed by the railway, are shown in the following table. This table shows clearly that the glacial streams abandon the higher points of their alluvial fans when they are built to a certain height, for at the time this railway leveling was done only one of the five fans had a stream upon its crest and that was a very small one. TABLE SHOWING A CROSS-SECTION- OF ALLTTVIAL FANS WEST or COPPER RIVER DELTA Position Elevation in Feet Position on Fan Distance in Miles Ascent or Descent in Feet Eastern alluvial fan East Sheridan stream 15 — — Small stream at Mile Post 17 49 Crest 2 +34 Near Mile Post 15 32.9 2 -16 Second alluvial fan Near Mile Post 14 43.9 Crest 1 +11 Main Sheridan Stream 32.9 * -11 Near Mile Post IS 31.5 4 -I* Third alluvial fan In Mile 12 42 Crest 1 + 10* Near Mile Post 11 28 i* -14 Fourth alluvial fan Near Mile Post 10 35 Crest * +7 Main Scott Stream 16 ii -19 Fifth alluvial fan Middle of Mile 7 20 Crest 1 +4 At Mile Post 7 15 4 -5 Middle of Mile 6 12.3 4 -«* Outlet of Eyak Lake 19.7 4 +74 This outwash gravel plain grades to fresh marsh, then to salt marsh, but in the area between the Copper River and the Sheridan Glacier streams the salt marsh extends up to the mountain base. Relation of OvJwash Deposits to Maintenance of the Railway. Two points stand out in connection with the building of the Copper River and Northwestern Railway on the Copper River delta. One is the ease of original construction upon these smooth alluvial fans, delta plain, and valley train, aside from the necessary filling 'm swamps and on quicksands. The other is the threat of expense of maintenance of the railway. The danger that the Sheridan Glacier might advance two and one-half miles and destroy the railway now seems practically negligible, but the danger that it may advance slightly and that the streams from it may shift and necessitate new trestles or may bury the track in places, as at Spencer Glacier on the Alaska Northern Railway,1 is an i i Tarr, R. 8. and Martin, Lawrence, An Experiment in Controlling a Glacial Stream, Annals Aasoc Amer. Geographers, Vol. n, 1912, pp. 25-40.